1. Technical Field
The present invention relates to a gas turbine, and in particular, to a gas turbine in which a cooling medium is supplied from a center hole of a rear portion shaft which is supported by bearing members having bearing member metals and wherein rotor blades of a turbine rotor are cooled by the cooling medium.
2. Prior Art
In general, a turbine rotor of a gas turbine has a structure in which plural turbine discs having rotor blades at an outer periphery thereof, are arranged in an axial direction, and to the most front portion side (an upstream side of a gas path which is a combustion gas flow passage of an inner portion of a turbine part) and to the turbine discs at a rear portion side a hollow pipe shape shaft portions are installed, respectively, and are combined as one body. Further a shaft portion of a rear portion side turbine disc, namely a rear portion shaft, is supported by bearing members having bearing member metals to a main body standstill or stationary side.
Gas turbines have had a tendency to heighten year by year the combustion temperature so as to improve an efficiency of the gas turbine. Accordingly, a rotor blade portion for recovering the energy of the combustion gas of a gas turbine rotor is exposed to the combustion gas having a higher temperature than a heat resistance temperature of the constituting materials of the rotor blade. Therefore, the compressed air generated by a compressor and the stream from a stream turbine are used as a cooling medium and this cooling medium is supplied in an interior portion of the rotor blade and a rotor blade portion is cooled.
In the conventional techniques, as a general rule there is an open cooling system in which a cooling medium after the cooling of the rotor blade is exhausted into the combustion gas.
Recently, with the aim of improving the utilization efficiency of the compressed air etc. and also for preventing the lowering of a turbine output, it has been proposed to have a closed cooling system in which the cooling medium after the cooling of the rotor blade is not exhausted into the combustion gas but is recovered in the interior portion of the gas turbine rotor and is reused as the combustion use air etc. Relating to this closed cooling system, as a recovery system of the cooling medium after the cooling, two systems have been developed. These are a system in which a recovery passage is provided at a front portion side of a turbine portion (hereinafter, called a “front portion recovery system”) and a system in which a recovery passage is provided at a rear portion side of the turbine portion (hereinafter, called a “rear portion recovery system”)
As the prior techniques of the front portion recovery system, there are the techniques shown in Japanese application patent laid-open publication Hei 11-50808 and Japanese application patent laid-open publication Hei 11-229804.
In the prior technique shown in Japanese application patent laid-open publication Hei 11-50808, an interior portion of a center hole of a rear portion shaft has a triple pipe structure in which two partitioning wall pipes having a large diameter and a small diameter of two different diameters are arranged in the same axial center position. A passage, which is formed in an interior portion of a small diameter partitioning wall pipe being positioned at the most center, is used as a supply passage of the cooling medium and a passage, which is formed between the small diameter partitioning wall pipe and a large diameter partitioning wall pipe, is used as an air passage for protecting bearing member metals from the heat of the cooling medium.
In the prior technique shown in Japanese application patent laid-open publication Hei 11-229804, as shown in FIG. 1 thereof, a rear portion shaft has a heat shield seal pipe which is arranged at a center hole thereof and a seal shaft which is arranged in series at a rear portion of the heat shield seal pipe. The heat shield seal pipe forms an air layer for protecting the bearing member metals from the heat of the cooling medium between an inner wall of the rear portion shafts. The seal shaft forms a labyrinth seal between opposed faces of a main body stationary side which encloses an outer wall thereof and prevents from leaking the cooling medium between the gas turbine rotor and the main body standstill side. The heat shield seal pipe and the seal shaft have respectively flanges and these flanges are installed through a bolt connection to a rear portion end face of the rear portion shaft.
As the front portion recovery system, there is Japanese application patent laid-open Publication Hei 7-189739, as shown in FIG. 1 thereof, to the most front portion side turbine disc, a recovery passage is provided and then a construction of a cooling medium recovery passage in an interior portion of a rear portion shaft can be omitted and then an interior portion structure is simplified.
However, in the above stated prior techniques, there are following problems.
In the prior techniques as the rear portion recovery system shown in Japanese application patent laid-open publication Hei 11-50808 and Japanese application patent laid-open publication Hei 11-229804, since the large partitioning wall pipe is arranged in the interior portion of the center hole of the rear portion shaft and plural medium passages (two passages of a supply use passage and a recovery use passage) are formed, inevitably it is necessary to have a large number of components and many connection portions thereof and the interior portion structure becomes complicated. Accordingly, assembly during the manufacture time becomes difficult. As a result, this requires a long period for manufacturing time and increases the cost.
In particular, in the prior technique shown in Japanese application patent laid-open publication Hei 11-50808, the two partitioning wall pipes have large size members and the front end portions of the two partitioning wall pipes form taper shape flange portions and connect them to a rear portion side turbine disc. Thus the above structure becomes complicated.
Further, the structure shown in Japanese application patent laid-open publication Hei 11-229804, since in the heat shield seal pipe and the seal shaft the flanges are provided respectively and the flange is bolt connected to the rear portion end portion of the rear portion shaft, in the rear portion shaft the vibrations due to a centering displacement can occur easily. Namely, normally in the bolt connection using the flange, to the rear portion shaft being a base side of the installation a female screw is formed and to the respective flanges to the heat shield seal pipe at an installing side and the seal shaft a bolt insertion hole being a larger diameter of the bolt (a unloaded hole) is bored. Accordingly, during the bolt connection since a space is formed inevitably between the bolt and the bolt insertion hole and in a radial direction, the above space in the radial direction is formed in both of the heat shield seal pipe and the seal shaft. As a result, during the high rotation time of the gas turbine rotor, according to the minute unbalance by them, a centering displacement can occur easily and then the vibrations are induced easily.
Further, in the structure of the prior technique shown in Japanese application patent laid-open publication Hei 11-229804, since the heat shield seal pipe fit-into contacts only at a tip end contact portion to the center hole of the rear portion shaft, in this contact portion, the heat shield seal pipe is fixed in the radial direction and then the heat shield seal pipe does undergo a centering displacement. However, at a rear end side at the flange portion only the bolt connection is carried out, in the rear portion side of the heat shield seal pipe the vibrations due to the centering displacement can occur easily.
Further, in the heat shield seal pipe, in the tip end portion thereof a ring shaped contact portion for contacting the inner wall of the rear portion shaft is formed, an outer diameter of the tip end contact portion thereof is difficult to manufacture with the complete circle but it cause the scattering within the tolerance. Accordingly, since the tip end contact portion does not contact uniformly to a whole periphery of the inner wall of the rear portion shaft, the several spaces are formed between the inner wall of the rear portion shaft and in the peripheral direction. When the spaces are formed, the cooling medium for passing through the interior portion of the rear portion shaft enters into the air layer and then the heat shield effect of the air layer lowers.
Further, when during the operation time the heat shield seal pipe is destroyed at an axial direction central position thereof, the portion to be subjected the destroy moves to the front portion and scatters to a front portion space and further collides with the turbine disc, as a result the big vibrations occur, according to circumstances there is a afraid of the turbine disc may destroy.
On the other hand, in the prior technique as the front portion recovery system shown in Japanese application patent laid-open publication Hei 7-189739, since the component number installed in the interior portion of the rear portion shaft is lessened and the structure is simplified, the vibrations due to the centering displacement can be reduced. However, in this prior technique, the construction of the bearing member metals for protecting the heat of the cooling medium has not studied.
In generally, the heat resistance temperature of the bearing member metal is 100 C.-150 C. degree and when it exceeds over the heat resistance temperature there is an afraid of the fusion of the bearing member metal. However, in many cases before the cooling of the rotor blade the heat temperature of the cooling medium to be supplied is more than (about more than 200 C) the heat resistance temperature and when this heat is transmitted to the bearing member metal from the interior portion of the rear portion shaft there is a possibility in which the temperature of the bearing ember metal exceeds over the heat resistance temperature.
Further, the above stated problem will occur in the case of the open cooling system, accordingly when the construction for protecting the bearing member metal is studied, it is necessary to consider the simplification of the structure, the prevention of the generation of the vibrations, the lowering of the heat shield effect, and the scattering during the heat shield component destroy time, etc.